1) Field of the Invention
The present invention relates to an optical module and an optical switch device suitable for use in an optical communication system.
2) Description of the Related Art
Since SOAs (Semiconductor Optical Amplifiers) are capable of operating at high speeds as optical switches, their application as optical switching elements for switching optical paths at high speeds has been regarded as promising. It is possible for a single SOA to operate as an optical gate switch, that is, a 1×1 optical switch. Further, multiple (n-number of) SOAs arranged in parallel function as an n×1 (or 1×n) optical switch 100 as shown in FIG. 19.
Here, the optical switch 100 in FIG. 19 is formed by an optical gate array 101, an optical coupler 102, and SOAs 103. These are provided as separate optical modules and are optically connected by means of optical fibers. The optical gate array 101 includes n (“8” in FIG. 19)-number of SOAs 101a, forming the optical gate array 101, arranged in parallel. Optical isolators 104a and 104b are arranged at the input and the output terminal of each of the SOAs 101a forming the optical gate array 101, and also, optical isolators 104c and 104d are arranged at the input and the output terminal of the SOA 103.
With this arrangement, when the optical switch 100 of FIG. 19 is given as an 8×1 optical switch, eight SOAs 101a of the optical gate array 101 let one of the eight beams of input light input through the isolator 104a pass through the optical switch to the optical coupler 102, while blocking other beams of input light. The optical coupler 102 outputs the light from the optical gate array 101 to the SOA 103, which appropriately amplifies the light from the optical gate array 101 in order to compensate for optical loss which has been caused when the light passes through the optical coupler 102.
Further, when the optical switch 100 of FIG. 19 is constructed as a 1×8 optical switch, the input and the output are inversed. That is, the SOA 103 amplifies light input through the optical isolators 104d, and the optical coupler 102 divides the light into eight outputs. Then, the eight SOAs 101a of the optical gate array 101 receive the eight beams of light divided by the optical coupler 102, respectively, and let one of the eight light beams pass therethrough to the optical isolator 104a side, and block the other light.
In this instance, the optical isolators 104a through 104d let only light proceeding from the optical gate array 101 to the SOA 103 pass therethrough, and block light proceeding in the opposite direction. As a result, reflection light is prevented from returning back to the SOAs 101a and 103, whereby laser oscillation is prevented.
That is, when the optical isolators 104a through 104d functions as the 8×1 optical switches 100, they let light proceeding from the optical gate array 101 to the SOA 103 pass therethrough and block light proceeding from the SOA 103 to the optical gate array 101. In contrast, the optical isolators 104a through 104d for the 1×8 optical switches 100 let light proceeding from the SOA 103 to the optical gate array 101 pass therethrough, and block light proceeding from the optical gate array 101 to the SOA 103.
Further, the following non-patent documents 1 and 2 show the publicly known arts relating to the preset invention:
(Non-patent Document 1) IEEE Photonic Technology Letters Vol. 10, No. 1, pp 162-164 (1998) Single-Mode to Multi-mode Combiner
(Non-patent Document 2) Optical Fiber Communication Conference PD4. 1-4. 4 1998 Title: “Lossless Hybrid Integrated 8-ch Optical Wavelength Selector Module Using PLC Platform and PLC-PLC Direct Attachment Technique”
However, according to the art of FIG. 19, to realize good amplification characteristics of the SOAs 101a of the optical gate array 101 and of the SOA 103, optical isolators need to be arranged over optical propagation paths. Thus, the number of components is increased, thereby increasing the device cost. Further, as optical insertion loss is increased, improvement in optical switch characteristics is prevented.
In particular, optical communication systems can include optical switches having such semiconductor amplifiers connected in multiple stages. In such optical switches, the number of components is thus increased, resulting in increase in the cost of the device, and optical insertion loss due to increase in the number of optical components is also increased.